Effects of the Ionic Liquid 1-Butyl-3-methylimidazolium Chloride on the Growth and Ethanol Fermentation of Saccharomyces cerevisiae AY92022

S. Zhu, P. Yu, Y. Tong, R. Chen, Y. Lv, R. Zhang, M. Lei, J. Ji, Q. Chen and Y. Wu

Abstract
Use of ionic liquids has provided a potential effective alternative in the conversion of carbohydrates in lignocellulosic materials into fermentable sugars for ethanol production. To evaluate how the remained ionic liquids in the fermentable sugars affect the subsequent ethanol fermentation process, the effects of ionic liquid 1- butyl-3-methylimidazolium chloride ([Bmim]Cl) in the medium at different concentrations from 10–3 to 1 g L–1 on the morphological structure, growth and ethanol fermentation of the yeast Saccharomyces cerevisiae AY92022 were investigated and compared with the control. First, the morphological structures of the yeast at different [Bmim]Cl concentrations were observed under an optical microscope. The results show that its single cell morphology remained unchanged at all [Bmim]Cl concentrations, but its reproduction rate by budding decreased with the [Bmim]Cl concentration increasing. Then its growth during ethanol fermentation process at different [Bmim]Cl concentrations was examined. The results indicated that the ionic liquid [Bmim]Cl inhibited the yeast growth. Its specific growth rate during the log phase and bacterial concentration during the stationary phase all decreased with the increase of [Bmim]Cl concentration. Finally, the ethanol fermentation process at different [Bmim]Cl concentrations was investigated and the results demonstrated that the ionic liquid [Bmim]Cl had a negative effect on ethanol production. When the [Bmim]Cl concentration increased, the final ethanol concentration and its yield from the fermentable sugars decreased, the finally remaining fermentable sugars increased, and it is interesting the ethanol specific formation rate at stationary phase remained unchanged at all [Bmim]Cl concentrations. It was also observed that when the [Bmim]Cl in the medium was 10–3 g L–1, the ethanol fermentation process data was almost no different to that of the control. This suggests that the [Bmim]Cl in the fermentable sugars should be controlled below 10–3 g L–1, thus it would not affect the subsequent ethanol fermentation process.

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Keywords
ionic liquid, [Bmim]Cl, growth, ethanol fermentation, Saccharomyces cerevisiae AY92022